UV curable coating composition

ABSTRACT

Disclosed is a method of coating an inkjet print head using a UV curable coating composition containing a (methyl)acryloxy or vinyl functionalized silane, silica and acrylate oligomer containing at least two acrylate groups.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a divisional of application Ser. No. 10/837,481,filed Apr. 29, 2004, now U.S. Pat. No. 7,183,353 hereby incorporated byreference.

The present invention relates to a UV curable coating composition, amethod for coating a substrate with said curable coating composition,and a substrate comprising a layer obtained by curing of said UV curablecomposition.

BACKGROUND

Electronic circuitry in the region of the interconnection between a dieand a flexible circuit on print head assemblies is prone to corrosion.The rate of corrosion is accelerated by the presence of ink, whichaccumulates in this region following the wiping of the nozzle plate toensure good print quality. The interconnect region on print heads iscommonly protected by the application of a polymeric protective layer,which is also known as encapsulant layer (see, US Patent Application2003/0017341 or U.S. Pat. No. 6,439,698). While these materials showgood resistance to ink permeation, with inks becoming increasinglycorrosive, problems are experienced with penetration of ink at theencapsulant/print head interface, which can lead to device failure.

Inorganic materials such as silica, alumina and tantala are known toproduce efficient protective layers. However, these materials cannot beselectively deposited onto the interconnect region at this stage(connection of the print head to the flexible circuit) of the print headassembly process.

For other parts of ink jet print heads, the use of layers comprisingcured polymer material is known. The use of photoimageable layerscontaining epoxy functional and methacryloxy functional silanes toproduce channel structures, jet plates, reservoirs, ink filters andpassivation layers of a print head is disclosed in U.S. Pat. No.6,312,085. Similar materials are also used in U.S. Pat. No. 6,283,578for the preparation of hydrophobic coating layers to control the wettingof ink on the surface of ink jet nozzle plates). The coating materialsdescribed in U.S. Pat. Nos. 6,283,578 and 6,312,085 require a longthermal curing step at elevated temperature in order to effectivelycross-link the silanol groups which are present in the materials aftercuring by ultraviolet (UV) light. This long processing time rendersthese materials unsuitable for applications in which automatedmanufacturing processes, such as reel-to-reel processing, are employedthat do not allow extended waiting times.

Furthermore, U.S. Pat. No. 5,910,372 discloses the use of a formulationbased on a mixture of silanes with different functional groups for thepreparation of hydrophobic coating layers on ink jet nozzle plates.Silanes containing amino groups are incorporated to improve adhesion tothe nozzle plate, which is made of polyimide, while perfluoroalkylsubstituted silanes are included to provide the required level ofhydrophobicity. This patent advances an earlier technology described inU.S. Pat. No. 5,121,134 in which the materials were applied separatelyin two coating steps. These materials also require a long thermal curingstep at elevated temperature which makes them unsuitable for use inmanufacturing processes such as reel-to-reel processing.

Problems are experienced with ink penetration to the interconnectionregion being enabled by delamination of the protective layer from thevarious surfaces present on the print head. Delamination allows ink aready path to the interconnect region by diffusion at the interfacebetween the protective layer and the print head. These problems arebecoming more difficult to overcome as ink formulations become moreaggressive, while at the same time increased levels of productreliability are expected.

Accordingly, there remains the need for a coating material that showslow ink uptake, thus limiting the penetration of ink through thisprotective coating. Such a coating should also show good adhesionproperties to the various surfaces present on a print head and itsadhesion should not be degraded by exposure to ink.

SUMMARY

In one aspect, a UV curable coating composition is provided. Thecomposition includes a (meth)acryloxy or vinyl functionalized silane,silica and an acrylate oligomer, wherein the acrylate oligomer containsat least two acrylate groups.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be better understood with reference to the detaileddescription when considered in conjunction with the examples and thedrawings, in which

FIG. 1 shows 3-methacryloxypropyl trimethoxysilane (FIG. 1 a) and3-acryloxypropyl trimethoxysilane (FIG. 1 b) and vinyl triethoxysilane(FIG. 1 c) as examples of suitable functionalized silanes that can beused in the coating composition in accordance with an embodiment of theinvention.

FIG. 2 shows a flow chart that illustrates a method of preparing acoating in accordance with an embodiment of the present invention.

FIG. 3 shows a flow chart that illustrates a method of coating aselected surface in accordance with an embodiment of the presentinvention.

FIG. 4 shows a cross-sectional view of a portion of an ink jet cartridge(also known as ink jet pen) onto which a coating obtained from a curablecoating composition in accordance with an embodiment of the invention isapplied.

DETAILED DESCRIPTION

The coating compositions of the invention are based on a(methyl)acryloxy or vinyl functionalized silane (which will be referredto as functionalized silane in the following) which after hydrolysis ofthe hydrolyzable groups of the silane and curing, provides the basicmatrix of the coating. In principle any suitable silane, alone or incombination with other silanes, can be used that has the formula (I)X_(a)SiY_(b),R^(X) _((4-a-b))  (I),

wherein in formula (I)

X denotes a hydrolysable group,

Y denotes a substituent that carries a vinyl, methacryloxy or acryloxyfunctionality;

R^(X) is alkyl, aryl, alkenyl, alkylaryl or arylalkyl,

a=1 to 3;

b=1 or 2.

Examples of a hydrolysable group are halogen atoms such as chloro orbromo atoms or —OR groups, i.e. alkoxy groups, aryloxy groups,alkylaryloxy groups or arylalkyloxy groups. Examples of groups that canbe used as substituent Y are vinyl groups, acryloxyalkyl groups ormethacryloxyalkyl groups.

One class of suitable (meth)acryloxy functionalized silanes has thechemical formula (II)

wherein in formula (II) R¹, R², and R³ are independently from each otherO-alkyl, O-aryl, O-arylalkyl, or halogen (Cl, Br, I, F) and R⁴ ishydrogen or methyl. In this connection, it is noted that alkyl and arylgroups in the functionalised silane usually have 1 to 20 carbon atoms.Alkyl groups can be straight chained or branched. Examples of alkylgroups are methyl, ethyl, propyl, isopropyl, butyl, isobutyl, tertiarybutyl, pentyl, isopentyl, neopentyl, hexyl, heptyl, octyl, nonyl groupsand the like. Examples for aryl groups are phenyl, naphthyl. Examplesfor arylalkyl groups are toluoyl or xylyl, while benzyl is an examplefor an alkyl aryl group.

One class of suitable vinyl functionalized silane compounds has thechemical formula (III)

wherein in formula (III) R¹, R², and R³ are independently from eachother O-alkyl, O-aryl, O-arylalkyl, or halogen (Cl, Br, I, F), whereinalkyl and aryl are defined above with respect to the compounds offormula (II). Examples of particularly suitable alkyl groups are methyl,ethyl, propyl, and isopropyl, whereas phenyl is an example of aparticularly suitable aryl group that can be present in the compounds offormula (II).

Examples of functionalized silane compounds that can be used in thecoating composition of the invention are 3-methacryloxypropyltrimethoxysilane (cf. FIG. 1 a), 3-acryloxypropyl trimethoxysilane (cf.FIG. 1 b), 3-methacryloxypropyl triethoxysilane, 3-acryloxypropyltriethoxysilane, 3-methacryloxypropyl tritert-butyloxysilane,3-acryloxypropyl tritert-butyloxysilane, 3-methacryloxypropyldimethoxethoxysilane, 3-acryloxypropyl-dimethoxethoxysilane,3-methacryloxypropyldiethoxmethoxysilane,3-acryloxypropyldiethoxmethoxysilane, vinyl triethoxysilane (cf. FIG. 1c), vinyl trimethoxysilane, or vinyl tris(2-methoxyethoxy)silane.

Silica is a second component in the curable composition of anembodiment. Incorporation of silica into the curable composition allowsthe deposition of thicker coating layers that do not crack, i.e. thathave a better mechanical strength. Any kind of silica particles can beused, as long as these particles are compatible with the process ofproducing the curable composition and with its deposition and curing onthe selected substrate. Examples of suitable silica particles are fumedsilica or colloidal silica. The silica particles can have a size rangingfrom 5 to about 200 or up to about 500 nanometers. Colloidal silica(Chemical Abstracts Number 7631-86-9) has been found to be particularlyuseful and is commercially available from many suppliers. For example,it is sold under the trade name Snowtex® from Nissan Chemicals or underthe trade name NYACOL® from Nyacol Nanotechnologies, Inc. The silicaused may have any available particle size and form. Typically, theparticles of the used silica have an average particle size or particlesize distribution ranging from about 5 to about 100 nanometers. In oneembodiment, the silica particles have a particle size in the range offrom about 10 to about 20 nanometers.

The curable composition further includes an acrylate oligomer. Additionof such an oligomer was found to improve the resistance of the curedcoating to degradation by ink. The acrylate oligomer contains at leasttwo acrylate groups (which are also referred to as functionalities). Theacrylate oligomer may thus have any number of acrylate functionalitiesfrom two or more, as long as the acrylate oligomer is compatible withthe other components of the coating composition and leads to a coatingwith acceptable chemical and mechanical properties.

Typically, the acrylate oligomer has two to six acrylatefunctionalities, meaning that the acrylate oligomer contains, forexample, two, three, four or six acrylate groups that can becross-linked when curing the coating composition disclosed herein. Theacrylate oligomer can be any aliphatic or aromatic branched orstraight-chained acrylate product. The oligomer can be an individualoligomer of a defined molecular weight, or an oligomer having amolecular weight distribution. It can be made from each a singlebuilding block or monomer for the isocyanate component (which can betolylenediisocyanate or hexamethylendiisocyanate, for example) and thecomponent having active hydroxyl groups (for instance 1,4butyleneglycol, or a polyether based on 1,2-ethyleneglycol). A mixtureof different building blocks for each of the isocyanate component andthe component having hydroxyl group can also be present in the acrylateoligomer. Mixtures of two or more chemically different acrylateoligomers can also be used in the composition.

Examples of suitable acrylate oligomers are urethane (meth)acrylateoligomer, epoxy (meth)acrylate oligomer, polyester (meth)acrylateoligomer, polybutadiene (meth)acrylate oligomer or melamine acrylateoligomer. Such an acrylate oligomer can be used alone or in combinationwith any other suitable acrylate oligomer. The acrylate oligomer can bechosen empirically such that chemical resistance, water resistance andheat resistance of the resulting coating are improved.

In accordance with the above explanations, useful acrylate oligomers caninclude a polyester backbone, a polyether backbone or a combinationthereof. A useful class of acrylate oligomers are urethane acrylateoligomers. Examples of such urethane acrylates that can be used in thepresent invention are those oligomers from Sartomer Company, Inc, Exton,Pa. that are available under the CN-Series or the Riacryl materials, forexample, Sartomer CN 991, CN 980, CN981, CN962, CN 964, SartomerCN973J85 or Sartomer Riacryl 3801 etc. For example, CN 981 and CN 980are aliphatic linear ethers, with a weight average molecular weight ofabout 1600 to about 1800 and about 2400 to about 2600, respectively. CN964 is a branched ester with a weight average molecular weight of 1600to 1800.

Other examples of suitable urethane acrylate oligomers are the linearpolyether urethane (meth)acrylate oligomers of the BR-500 series oraliphatic (difunctional) polyester urethane acrylate oligomers of theBR-700 series, or the aromatic and aliphatic trifunctional polyetherurethane (meth)acrylate oligomers of the BR-100 series all of which areavailable from Bomar Specialities Co., Winsted, Conn. The general classof urethane oligomers described in U.S. Pat. No. 5,578,693 can also beused in the composition of the invention.

Other examples of suitable acrylate oligomers are the melamine acrylateoligomers of the BMA series which are also available from BomarSpecialities Co. An example of a suitable polyester acrylate oligomer isthe oligomer CN294 available from Sartomer Company, Inc.

In one embodiment, an adequate acrylate oligomer has a weight averagemolecular weight in the range from about 1000 to about 6000 Dalton. Inanother embodiment, the acrylate oligomers have a weight ranging fromabout 1100-1300 to about 5400-5600.

A further component of the curable composition is a solvent. Inprinciple, any solvent can be used as long as it is miscible with theother components but chemically inert. Examples of useful solventsinclude ethanol, isopropanol, ethyl methyl ketone (EMK) or high boilingpoints solvents such as ethylene glycol, propylene glycol, propyleneglycol methyl ether, propylene glycol ethyl ether and other glycolethers.

In addition to the above-mentioned components, the curable compositioncan optionally include an adhesion improving agent. Depending on thenature of the part to be coated, a single adhesion improving agent (alsocalled adhesion promoting agent) or a combination of two or more of themcan be used. Such an agent can be a mercapto functionalizedalkoxysilane, an epoxy functionalized alkoxysilane or combinationsthereof. Mercapto functionalized alkoxysilanes have been found useful inparticular when surfaces that contain metals such as gold, copper,iridium, or palladium are to be coated since the sulfur group binds tothese metals. In so doing, not only is the wet adhesion strength of thecoating improved, but also the corrosion inhibition properties of thecoating.

Epoxy functionalized silanes bind well to polymeric surfaces such aspolyimide. Therefore, by use of epoxy functionalized silanes, thecoating adhesion on polymeric surfaces can also be markedly improved.Thus, combinations of a mercapto functionalized silane and an epoxyfunctionalized silane are typically employed when the part to be coatedwith the composition in accordance with an embodiment has both metallicand polymeric surfaces present.

Examples of suitable mercapto functionalized alkoxysilanes are3-mercaptopropyl trimethoxysilane or 3-mercaptooctyltrimethoxysilane.Examples of epoxy functionalized alkoxysilane are 3-glycidoxypropyltrimethoxysilane, 3-glycidoxypropyl trimethoxysilane, 3-glycidoxypropylmethyldiethoxysilane, or 3-glycidoxypropyl methyldimethoxysilane. Ifdesired, these adhesion improving agents can be present in thecomposition in a range of about 0.5 to 20 wt. % related to the totalweight of the composition. Typically, the weight percentage of theadhesion improving agent is then chosen such that the molar ratio of the(meth)acryloxy or vinyl functionalized silane to the adhesion improvingagent(s) varies in the range of 1.00:(0.01-0.50).

The above-described components are usually present in the curablecomposition in the following weight ratios (which are expressed asweight percent relating to the total weight of the composition; % w/w):

-   -   (methyl)acryloxy or vinyl functionalized silane: 25 to 50 wt.-%,    -   silica: 10 to 25 wt.-%,    -   acrylate oligomer: 4 to 15 wt.-%    -   solvent: 20 to 40 wt.-%;    -   adhesion improving agent (additive): 0.5 to 20 wt.-%

In some embodiments, the content of the components in the composition isas follows:

-   -   (methyl)acryloxy or vinyl functionalized silane: 30 to 42 wt.-%,        or 35 to 38 wt.-%,    -   silica: 13 to 21 wt.-%, or 16 to 18 wt.-%,    -   urethane acrylate oligomer: 4 to 15 wt.-%    -   solvent: 25 to 37 wt.-%, or 28 to 32 wt.-%;    -   adhesion improving agent (additive): 5 to 18 wt.-% or 6 to 14        wt.-%

Furthermore, for the curing step an initiator compound (catalyst) thatstarts the cross-linking between any of the vinyl, acrylate andmethacrylate groups within the coating is usually added to thecomposition. Since curing can be conveniently carried out by exposure toUV light, photoinitators that create free radicals upon irradiation withlight of respective wavelength are a presently preferred group ofcatalysts. Examples of suitable photoinitators include the compoundsmanufactured by Ciba, Switzerland under the trade names Darocur® andIrgacure®. Such initiator compounds are usually added to the compositionin small amounts, for example, 0.1 to 5 wt. % relative to the totalweight of the composition.

The composition can further include auxiliary agents which provide for afaster curing and/or an improved cross-linking of the vinyl and(meth)acrylate groups within the coating. Examples of such auxiliaryagents are monomeric compounds having two or more acrylatefunctionalities such as 1,4-butanediol dimethacrylate,trimethylolpropane triacrylate, pentaerythritol triacrylate, orditrimethylolpropane tetracrylate. If added, these auxiliary reagentsare generally present in small amounts, typically 0.1 to 10 wt. %related to the total weight of the composition.

FIG. 2 shows a method of preparing a composition in accordance with anembodiment. A first step 210 involves mixing silica with a solvent. Inan embodiment, a colloidal silica such as Snowtex O (Nissan Chemicals isutilized and examples of a suitable solvent include ethanol, isopropanolor mixtures thereof.

A second step 220 involves adding a functionalized silane to thesolution. Examples of suitable functionalized silianes include3-methacryloxypropyl trimethoxysilane or 3-acryloxypropyltrimethoxysilane. Here, the functionalized silane is added over a periodof time that is sufficiently long to prevent formation of cloudiness.Usually, the addition of the functionalized silane is carried outdropwise over a period of 10 to 20 minutes. If used in the compositionof the invention, the adhesion improving agent(s) such as mercaptoand/or epoxy functionalized alkoxysilane(s) (e.g., 3-mercaptopropyltrimethoxysilane 3-glycidoxypropyl trimethoxysilane) is/are usuallyadded to the reaction medium at the same time. The solution is thenallowed to react for an appropriate period of time (generally severalhours, for example about 1.5 or 2 hours to about 4 hours). During thisperiod siloxane oligomers containing mixtures of the three functionalgroups are generated in the solution. The molar ratio of the(meth)acryloxy or vinyl functionalized silane to the adhesion improvingagent can be varied in the range of 1.00:(0.05-0.50).

If epoxy functionalized alkoxysilane is present (alone or in combinationwith mercapto functionalized alkoxysilane) for improving the adhesionproperties, the molar ratio of the (meth)acryloxy or vinylfunctionalized silane to epoxy functionalized alkoxysilane can be variedin the range 1.00:(0.10-0.50). If mercapto functionalized alkoxysilaneis present (alone or in combination with epoxy functionalizedalkoxysilane) the molar ratio of the (meth)acryloxy or vinylfunctionalized silane to mercapto functionalized alkoxysilane is usuallyvaried in the range 1.00:(0.01:0.20). If members of these two classes ofadhesion promoting agent are used together, a presently preferred molarratio of functionalized silane to epoxy functionalized alkoxysilane andmercapto functionalized alkoxysilane is about 1.00:(0.33):(0.05). Duringthe subsequent coating step, these oligomers cross-link to form thecoating matrix.

A final step 230 includes adding an acrylate oligomer containing atleast two acrylate groups to the solution. In an embodiment, theacrylate oligomer is added in conjunction with a photoinitiator afterthe formation of the siloxane oligomers. The solution is then stirred todissolve the acrylate oligomers

An alternate embodiment is also contemplated whereby the so-obtainedcurable composition is applied on a selected surface. FIG. 3 shows aflowchart of a method of coating a selected surface. A first step 310involves applying on a surface a UV curable composition containing a(meth)acryloxy functionalized silane, silica and a acrylate oligomercontaining at least two acrylate groups. In an embodiment, the surfaceis a substrate. A final step 320 involves curing the appliedcomposition.

Dip coating, micro-spray coating, spin coating as well as needledispensing methods can been employed. Printing is also possible if theproperties of the formulation are modified by addition of rheologymodifiers. Suitable rheology modifiers are Aerosil fumed silicas, arange of which are supplied by Degussa AG, Düsseldorf, Germany. Spraycoating and printing may provide advantages in some cases since theyallow the coating composition (coating layer) to be applied selectivelyon specific areas of the surface where corrosion protection is required.

Coating thicknesses in the region of 1 to 20 microns are generallyemployed, though both thicker (for example up to 50 or 100 microns iftraces at the interconnect region of a print head are to be protected bythe coating) and thinner layers can be produced by adjustment of thecoating solution properties or the parameters of the depositiontechnique.

After application, the coatings are UV cured in order to convert thesurface to a tack free state. This step may be followed by a thermalconsolidation step at a sufficiently high temperature (about 150° C. toabout 200° C., for example) for a sufficiently long period of time,usually from several minutes to about one hour, to enhance the coating'smechanical properties and improve its chemical resistance. However, itis also possible to employ a longer curing time at a lower temperature.The actual conditions for the thermal curing also depend on processingconstraints and curing equipment and can be determined empirically. UVirradiation causes cross-linking of the vinyl, acrylate and methacrylategroups within the coating, while thermal treatment accelerates formationof the sol-gel silicate matrix through condensation of residual silanolgroups.

The coating composition shows good adhesion to a great variety ofsurfaces and thus allows the coating of a plurality of substrates. Thesubstrate may include any material that is selected from the groupconsisting of silicon, metal, glass and polymeric material. If apolymeric material is to be coated, this polymeric material may includeof polyimide, polycarbonate, poly(methyl)acrylate,acrylonitrile-butadiene-styrene (ABS), epoxide based polymers andcombinations thereof. Metals that can be coated with the compositioninclude gold, silver, palladium, iridium, platinum (i.e. the noblemetals), copper, iron, nickel as well as alloys and any combination ofsuch metals. The substrate can be, for example, part of any electroniccomponent or circuitry, where a protective layer is usually applied toprevent mechanical damage, e.g., by abrasion, or chemical degradation,e.g., by corrosion.

As can be seen from the above list of suitable materials, the coatingcan be applied on virtually every material that is used in surfacesareas of ink jet print heads or cartridges of ink jet printers.Therefore, the coating composition can be applied to form a protectivecoating on interconnect regions or layers such as epoxy based barrierlayers on ink jet printers, for example. The interconnect region may bethe region of the interconnections between a die and a flexible circuitof the print head. A coating made from the composition may also be usedas an undercoat prior to the application of a traditional encapsulantmaterial used to protect the print head. Applied on the respectivesurfaces of an ink jet print head, the cured composition providesprotection against ink ingress into the substrate and hence inhibitscorrosion thereof.

Therefore, in one embodiment the substrate to be coated is a print headon an ink jet cartridge. One example of a protective layer that isformed on parts of an ink jet cartridge using a composition is shown inFIG. 4. The cured coating composition provides a protective layer 454 inthe interconnect region 456 of an ink jet cartridge (or pen). Theinterconnect region 456 is the region between the orifice plate 420 ofan ink jet print head 412 and the tape automated bonding (TAB) circuit426, both of which are attached to the cartridge body 414. The orificeplate 420 includes nickel and the TAB circuit 426 is made from apolyimide film. The protective layer 454 covers the bond pads 436, 438and the wires or tape automated bonds (TAB) 440 and protects them fromcorrosion by ink which is expelled from nozzles (not shown) of theorifice plate 420. The coating composition is applied in such a mannerthat the protective coating is in contact with both the orifice plate420 and the TAB circuit 426.

As will also be seen from the following examples, coatings of theinvention show excellent adhesion to different surfaces present on thesurface of ink jet print heads. The coatings are also not affected byaccelerated aging tests. When immersed in ink at elevated temperature,coatings withstand up to 54 days exposure to ink at 60° C., thus makingthem very promising for use in large scale manufacture of ink jet printheads.

EXAMPLE 1

Snowtex O (9.0 g) was mixed with ethanol (11.0 g) in a glass beaker. Tothis mixture was added 3-methacryloxypropyl trimethoxysilane (19.8 g),3-glycidoxypropyl trimethoxysilane (6.6 g) and 3-mercaptopropyltrimethoxysilane (0.8 g) dropwise with stirring. After allowing thehydrolysis and condensation reactions to proceed for 2 hours, SartomerCN981 (6.8 g) was added and the solution was stirred until homogeneous.In the final step, Darocur 1173 photoinitiator (2 g) was added.

Using a dip coating process, with a sample retraction rate of 2 mmsec⁻¹, the coating solution was applied to tab head assemblies as wellas to uncoated glass microscope slides and larger samples of materialspresent on only small surfaces of the ink jet print head (i.e. 25×25 mmarea samples coated with epoxy formulations or plated with gold. Sampleswere UV cured by passage through a Technigraf GmbH (Grävenwiesbach,Germany) belt oven (80 W/cm, 3 m/min). Heating samples at 200° C. fortwo minutes completed the coating process.

Samples were stored in a sealed container filled with black ink at 60°C. At six day intervals, samples were removed from the ink, washed withdeionized water and blotted dry. Adhesion of the coating to thedifferent surfaces of interest was measured using cross hatch adhesiontesting.

EXAMPLE 2

Snowtex O (9.0 g) was mixed with ethanol (11.0 g) in a glass beaker. Tothis mixture was added 3-methacryloxypropyl trimethoxysilane (19.8 g)and 3-mercaptopropyl trimethoxysilane (0.8 g) dropwise with stirring.After allowing the hydrolysis and condensation reactions to proceed for2 hours, Sartomer CN981 (6.8 g) was added and the solution was stirreduntil homogeneous. In the final step, Darocur 1173 photoinitiator (2 g)was added.

EXAMPLE 3

Snowtex O (9.0 g) was mixed with ethanol (11.0 g) in a glass beaker. Tothis mixture was added 3-methacryloxypropyl trimethoxysilane (19.8 g)dropwise with stirring. After allowing the hydrolysis and condensationreactions to proceed for 2 hours, Sartomer CN981 (6.8 g) was added andthe solution was stirred until homogeneous. In the final step, Darocur1173 photoinitiator (2 g) was added.

EXAMPLE 4

Snowtex O (9.0 g) was mixed with ethanol (11.0 g) in a glass beaker. Tothis mixture was added 3-methacryloxypropyl trimethoxysilane (19.8 g)and 3-mercaptopropyl trimethoxysilane (0.8 g) dropwise with stirring.After allowing the hydrolysis and condensation reactions to proceed for2 hours, Sartomer CN980 (6.8 g) was added and the solution was stirreduntil homogeneous. In the final step, Darocur 1173 photoinitiator (2 g)was added.

EXAMPLE 5

Snowtex O (9.0 g) was mixed with ethanol (11.0 g) in a glass beaker. Tothis mixture was added 3-methacryloxypropyl trimethoxysilane (19.8 g),3-glycidooxypropyl trimethoxysilane (6.6 g) and 3-mercaptopropyltrimethoxysilane (0.8 g) dropwise with stirring. After allowing thehydrolysis and condensation reactions to proceed for 2 hours, SartomerCN980 (6.8 g) was added and the solution was stirred until homogeneous.In the final step, Darocur 1173 photoinitiator (2 g) was added.

EXAMPLE 6

Snowtex O (9.0 g) was mixed with ethanol (11.0 g) in a glass beaker. Tothis mixture was added 3-methacryloxypropyl trimethoxysilane (18 g) and3-mercaptopropyl trimethoxysilane (0.8 g) dropwise with stirring. Afterallowing the hydrolysis and condensation reactions to proceed for 2hours, trimethylolpropane triacrylate (2 g) and Sartomer CN981 (6.8 g)were added and the solution was stirred until homogeneous. In the finalstep, Darocur 1173 photoinitiator (2 g) was added.

EXAMPLE 7

Snowtex O (9.0 g) was mixed with ethanol (11.0 g) in a glass beaker. Tothis mixture was added 3-methacryloxypropyl trimethoxysilane (19.8 g)and 3-mercaptopropyl trimethoxysilane (0.8 g) dropwise with stirring.After allowing the hydrolysis and condensation reactions to proceed for2 hours, Sartomer CN973J85 (6.8 g) was added and the solution wasstirred until homogeneous. In the final step, Darocur 1173photoinitiator (2 g) was added.

EXAMPLE 8

Snowtex O (9.0 g) was mixed with ethanol (11.0 g) in a glass beaker. Tothis mixture was added 3-methacryloxypropyl trimethoxysilane (19.8 g)and 3-mercaptopropyl trimethoxysilane (0.8 g) dropwise with stirring.After allowing the hydrolysis and condensation reactions to proceed for2 hours, Sartomer CN973H95 (6.8 g) was added and the solution wasstirred until homogeneous. In the final step, Darocur 1173photoinitiator (2 g) was added.

EXAMPLE 9

Snowtex O (9.0 g) was mixed with ethanol (11.0 g) in a glass beaker. Tothis mixture was added 3-methacryloxypropyl trimethoxysilane (19.8 g),3-glycidooxypropyl trimethoxysilane (6.6 g) and 3-mercaptopropyltrimethoxysilane (0.8 g) dropwise with stirring. After allowing thehydrolysis and condensation reactions to proceed for 6 hours, most ofthe solvent was evaporated off using a rotary evaporator and wasreplaced by methyl ethyl ketone. Sartomer Riacryl 3801 (6.8 g) was addedand the solution was stirred until homogeneous. In the final step,Darocur 1173 photoinitiator (2 g) was added.

EXAMPLE 10 (COMPARATIVE EXAMPLE)

Snowtex O (9.0 g) was mixed with ethanol (11.0 g) in a glass beaker. Tothis mixture was added 3-methacryloxypropyl trimethoxysilane (19.8 g)dropwise with stirring. After allowing the hydrolysis and condensationreactions to proceed for 2 hours, Darocur 1173 photoinitiator (2 g) wasadded.

For examples 2 to 10, coatings were prepared and samples tested usingthe same procedures as outlined in Example 1.

RESULTS

Coating performance was measured by conducting adhesion tests aftersoaking parts in ink. A cross-hatch pattern approximately 2 cm×2 cm insize was cut in the coated substrate using a Stanley knife. Tape (Scotch898, 3M) was then applied to the pattern and pulled off again in a slowcontrolled fashion, removing the tape at an angle of 90° to thesubstrate surface. A qualitative measure of coating adhesion wasobtained by observing what percentage of the coating is removed on thetape.

This test was carried out on all the surfaces of interest in theinterconnect region both before and after exposure of the samples to inksoak. Ink soak testing was carried out by placing coated substrates intoa sealed bottle of ink, which was then stored in an oven at 60° C. for 6days. The ink used was Hewlett Packard 51645a black ink. If coatingswithstood the tape test after 6 days, samples were returned to the inkfor further testing. Results of cross-hatch testing are shown in Table1.

TABLE 1 Polyimide Gold coating No. of days coating No. of days removedink soak removed ink soak after 6 before >5% after 6 before >5% days inkcoating days ink coating Example soak (%) removed soak (%) removed 1 036-48 0 >54 2 5-10  6-12 0 >30 3 20-30  6 0 6 4 20-30  6 0 >6 5 20-30  65-10  6 6 5-10 6 0 >6 7 5-10 6 0 >6 8 5-10 6 0 >6 9 0 36 0 24 10(Comparative 100 6 100 6 Example)

As can be seen from Table 1, the composition results in coatings thatshow a good adhesion and resistance to long-term exposure of ink,whereas a coating that does not contain acrylate oligomers, is alreadycompletely removed after 6 days of testing under the same conditions,indicating an inferior adhesion.

The various modifications and alterations of this invention will beapparent to those skilled in the art without departing from the scopeand spirit of this invention. The invention should not be restricted tothat set forth herein for illustrative purposes.

1. A method for coating an inkjet print head with a protective layercomprising: applying on an inkjet print head a UV curable compositioncomprising: (a) 25% to 50% by weight (meth)acryloxy or vinylfunctionalized silane, (b) 10% to 25% by weight silica, (c) 4% to 15% byweight acrylate oligomer containing at least two acrylate groups, and(d) 20% to 40% by weight solvent; and curing the composition.
 2. Themethod of claim 1, wherein the coating provides protection in a regionof interconnections between the inkjet print head and a flexiblecircuit.
 3. The method of claim 1, wherein the coating composition isapplied on the inkjet print head by a method selected from the groupconsisting of micro-spray application, dip coating, spin coating,printing and needle dispensing application.
 4. The method of claim 1,wherein the (meth)acryloxy functionalized silane has a chemical formula

wherein in formula (I) R¹, R², and R³ are independently from each otherO-alkyl, O-aryl, O-arylalkyl, or halogen and R⁴ is hydrogen or methyl,and wherein the vinyl functionalized silane has the chemical formula

wherein in formula (II) R¹, R², and R³ are independently from each otherO-alkyl, O-aryl, O-arylalkyl, or halide.
 5. The method of claim 1,wherein the silica is selected from the group consisting of colloidalsilica and fumed silica.
 6. The method of claim 5, wherein the colloidalsilica has a particle size ranging from about 5 to 100 nanometers. 7.The method of claim 1, wherein the acrylate oligomer is selected fromthe group consisting of urethane (meth)acrylate oligomer, epoxy(meth)acrylate oligomer, polyester (meth)acrylate, polybutadiene(meth)acrylate oligomer, and melamine (meth)acrylate oligomer.
 8. Themethod of claim 1, wherein the urethane acrylate oligomer comprises abackbone selected from the group consisting of a polyester backbone,polyether backbone or a combination thereof.
 9. The method of claim 1,wherein the acrylate oligomer has a weight average molecular weightranging from about 1000 to about 6000 Dalton.
 10. The method of claim 1,further comprising an adhesion improving agent present in an amount of0.5% to 20% by weight based on the total weight of the composition. 11.The method of claim 10, wherein the adhesion improving agent is selectedfrom the group consisting of mercapto functionalized alkoxysilane, epoxyfunctionalized alkoxysilane or combinations thereof.
 12. An inkjet printhead comprising a coating layer obtained by curing a UV curablecomposition comprising a) 25% to 50% by weight (meth)acryloxy or vinylfunctionalized silane b) 10% to 25% by weight silica c) 4% to 15% byweight acrylate oligomer containing at least two acrylate groups and d)20 to 40% by weight solvent.
 13. The inkjet print head of claim 12,wherein the (meth)acryloxy functionalized silane has a chemical formula

wherein in formula (I) R¹, R², and R³ are independently from each otherO-alkyl, O-aryl, O-arylalkyl, or halogen and R⁴ is hydrogen or methyl,and wherein the vinyl functionalized silane has the chemical formula

wherein in formula (II) R¹, R², and R³ are independently from each otherO-alkyl, O-aryl, O-arylalkyl, or halide.